Optical fiber cables for transmitting high optical power are frequently used in industrial applications. Specifically they are used in cutting and welding operations by means of high-power laser radiation, but also in other industrial applications such as heating, detection or working operations in high temperature environments this type of high power optical fiber cables can be used.
Due to the all increasing laser power which is used today—together with an all increasing radiation quality—the requirements on the optical components in the system to really sustain the high power have also been increased. The optical components must provide a high stability with respect to focal lengths, focusing quality etc. For that reason, it is often necessary to cool down the optical components in order to maintain the necessary stability. The present invention relates to a device for providing a more efficient cooling capacity compared to previous designs.
The main reason for instabilities in the optical system is the heating. Heating is not only effecting the optical components as such but also the housing in which the optical components are mounted. In this case the heating from the housing is transmitted by radiation and convection to the optical components so that they are also heated. One reason to the heating is the uncontrolled radiation existing around the radiation beam itself and which might hit a mechanical detail such as the optical lens holder so that this mechanical component is heated. Another reason is the heating generated due to radiation impinging upon the lens itself and which is reflected back due to imperfections on the anti-reflex treated lens surface or due to particles on the lens surface. Such back-reflected, uncontrolled radiation might also generate a heating effect on the housing. If the housing is heated, as a secondary effect, also the optical components might be heated by radiation or convection. In addition to these processes there is also a certain absorption in the lens material.
The traditional technique to take care of such unwanted heating effect is to cool down the holder itself in which the optical components are mounted. A holder, preferably made of a material having a good heat conducting capacity, such as aluminum, is used for the housing of the optical components. Outside this housing it is arranged a cooling device filled with a flowing coolant, preferably water. The cooling device is made of a material which should not be effected by the coolant, for instance acid-proof stainless steel. In order to minimize the heating resistance between the cooling device and the housing the wall of the housing is made thin and a glue with a good heat conducting capacity is used for the mounting.
As an alternative, the cooling device might be arranged in a direct contact with the housing so that the coolant is flowing in canals directly on the housing. Also in this case the housing is made of a material with a good heat conducting capacity. The advantage with this method is a more efficient cooling effect, but as the coolant is in direct contact with the heat conducting material, usually aluminum, this design might cause corrosion problems, if not specific corrosion inhibitors are added to the flowing coolant.
In order to avoid high temperature gradients in the system, preferably a material with a good heat conducting capacity, such as aluminum, should be used. However, such materials normally also have a high heat expansion coefficient with inherent mechanical deformations which might easily cause optical instabilities.
As to cooling an optical fiber, it is previously known by SE 509 706 to have at least one of the contact ends of the fiber located in a cavity filled with a flowing coolant so that radiation falling outside the fiber is entered into and absorbed at least partially by the coolant. For optical components mounted in some type of housing or holder this type of direct cooling cannot be used.